1. Field of the Invention
The present invention relates to a lens barrel, more specifically to a retraction mechanism of a lens barrel for retracting the lens barrel when no pictures are taken.
2. Description of the Related Art
In a retractable lens barrel for a camera that reduces the length thereof in a non-photograph state (accommodated state/retracted state) for the purpose of miniaturization of the camera, specifically for reduction in thickness of the camera, a further reduction in length of the lens barrel in the retracted state has been desired. For instance, in the photographic lenses of lens shutter cameras, it is often the case that a light quantity control unit including a shutter and an adjustable diaphragm is supported by a support member via a lens group holding frame. Although a light quantity control component such as a set of shutter blades or diaphragm blades must be located at optically designed positions at a time of exposure, the light quantity control component becomes free from the optical constraints thereon when the lens barrel is in the retracted state, and accordingly, the length of the lens barrel in the retracted state can be reduced by bringing the light quantity control unit close to an adjacent lens group in the optical axis direction when the lens barrel is fully retracted. The assignee of the present invention has proposed a retraction mechanism of a lens barrel using such a technique in United States Patent Application Publication No. US 2005/0207748 A1 (Japanese Patent Application Publication No. 2005-266345).
In the lens barrel disclosed in United States Patent Application Publication No. US 2005/0207748 A1, a retractable lens group support ring (second lens group support ring) which holds a shutter unit is linearly guided by a linear guide ring, and the movement of the retractable lens group support ring in the optical axis direction is controlled via a cam ring. This retractable lens group support ring is provided therein with a rotatable lens frame (i.e., a radially-retractable lens frame) which holds a lens group. The rotatable lens frame is linearly guided so as to be relatively movable in the optical axis direction along an eccentric pivot. In a ready-to-photograph state, the rotatable lens frame is held inside, and at the rear end of, the retractable lens group support ring. During a lens barrel accommodation operation (in which the lens groups of the lens barrel are retracted rearwardly to an accommodated state), upon the retractable lens group support ring moving rearwardly in the optical axis direction, firstly, the retractable lens group support ring and the rotatable lens frame move rearwardly together until the rotatable lens frame abuts against a position-control cam provided at a rearward position. Upon the rotatable lens frame abutting against the position-control cam, the rotatable lens frame rotates from a ready-to-photograph position on the optical axis to a radially-retracted position while the rearward movement of the rotatable lens frame is controlled by the position-control cam. Thereafter, further rearward movement of the retractable lens group support ring in the optical axis direction causes the rotatable lens frame to move forwardly, relative to the retractable lens group support ring so as to change (reduce) the distance in the optical axis direction between the shutter unit and the lens group. With such operations, a reduction in length of the lens barrel is achieved. Meanwhile, in the case of making the lens barrel perform a retracting operation using pressing forces due to relative contact between such front and rear optical element holding members, each of these optical element holding members is required to move smoothly without inclining or tilting relative to the original moving direction thereof (optical axis direction). Specifically, in the case where the front and rear optical element holding members are biased forward or rearward in the optical axis direction, the actuation capability of the front and rear optical element holding members needs to be improved by examining the effects of the biasing force applied to the front and rear optical element holding members.